This invention relates to a semiconductor device, and more particularly to a semiconductor device with a multielectrode construction equivalent to a variable capacitance diode, thereby being capable of extending a change in capacitance.
In general, a p-n junction diode is used as a variable capacitance diode because, when a reverse-bias is applied to the p-n junction, the carriers in the vicinity of the junction are moved to induce a depletion layer and the width of the resulting depletion layer is characteristic of depending upon the reverse-bias voltage.
The conventional variable capacitance diode has an essential construction such that an electrode applied with a bias voltage thereto functions as an electrode for reading out a change in capacitance therefrom in itself. Consequently, if a bulk having a uniformly distributed carrier concentration is provided, a C-V characteristic of the diode will represent a relatively gentle change in capacitance under a high reverse-bias condition and, therefore, it may be necessary to control a diffusion profile, for example by ion-implantation. This means that the production of devices may encounter a difficulty and, if possible, the control thereof may be limited within a narrow range. Also, for the sake of the construction as described above, it is an disadvantage that the degree of freedom is relatively small in a circuit design. Further, since the conventional variable capacitance diode is such that the depletion layer induced by the movement of carriers is limited in its width, a ratio of a maximum capacitance Cmax to a minimum capacitance Cmin is nothing mre than a relatively small value of about 20.